An HF vapor etch etches high aspect ratio openings to form MEMS devices and other tightly-packed semiconductor devices with 0.2 um air gaps between structures. The HF vapor etch etches oxide plugs and gaps with void portions and oxide liner portions and further etches oxide layers that are buried beneath silicon and other structures and is ideally suited to release cantilevers and other MEMS devices. The HF vapor etches at room temperature and atmospheric pressure in one embodiment. A process sequence is provided that forms MEMS devices including cantilevers and lateral, in-plane electrodes that are stationary and vibration resistant.